1. Field of the Invention
The present invention relates to a bipolar plate structure having optimized gas flow channels, especially for a metal bipolar plate of a fuel cell to allow the fuel gas, oxidant, coolant and the like to be evenly distributed on a specific gas flow path plane, so as to improve corrosion resistance and mechanical strength of the bipolar plate and increase the life of the fuel cell.
2. Description of Related Art
As the traditional petrochemical energy has been gradually depleted and the use of petrochemical energy makes a significant impact on the ecological environment, governments around the world have turned to the development of low-pollution and energy-efficient energy sources. Among the new developed energy sources including solar cells, biochemical energy, fuel cells, and the like, the fuel cells have attracted attention due to having a high power generation efficiency of about 60% and low pollution.
A fuel cell is a power generation device that directly converts the chemical energy from a fuel into electricity through an electrochemical reaction of hydrogen-containing fuel (e.g. methanol, ethanol, hydrogen, and the like) with oxygen or other oxidants. In addition to electricity, fuel cells also produce a by-product of water. Compared with the traditional power generation methods, the fuel cell has the advantages of low pollution, low noise, and high energy conversion efficiency. Moreover, electricity of the fuel cell is directly converted from oxidation reactions of the fuel, so its discharge current increase as the fuel supply increases and it can continuously generate electricity as long as the fuel and oxygen are fully supplied. Accordingly, the fuel cell does not have the problems of power outage, charging and pollution.
Generally, a fuel cell is constituted by a membrane electrode assembly (MEA) and electrode plates. The MEA is referred as a core of the fuel cell for electrochemical reactions, and the electrode plate is one of the key factors influencing the commercialization of fuel cell. There are many problems of electrode plate material, flow field structure or processing cost of the fuel cell to be solved.
Specially, the traditional electrode plate is mainly made from graphite, composite carbon and metal substrates. For the electrode plate formed of the graphite and the composite carbon material, it has the advantages of conductivity and corrosion resistance, but its manufacturing process is complicated and time consuming. Moreover, the electrode plate formed of the graphite and the composite carbon material has a thickness of not less than 3 mm, which is not conducive to the miniaturization of the fuel cells. For the electrode plate formed of the metal substrates, it has the advantages of a less thickness and a light weight to reduce the volume and the weight of the fuel cells. However, this kind of fuel cell made from the metal electrode plates has lower electricity production efficiency due to a low transport capacity of flow ducts on the metal electrode plates.
For instance, the Taiwan patent TWI476986 (B), issued on 11th Mar. 2015, disclosed a fuel cell stack and its partition plate. The partition plates having identical structure are used in an anode electrode and a cathode electrode plate of a fuel cell to reduce the manufacturing costs of the fuel cell. The partition plate is mainly provided with a gas flow channel surface formed by impact molding and a corresponding coolant flow channel surface. An arrow-shaped block formed by the gas flow channel surface allows the fuel gas and the oxidant to be evenly distributed on the gas flow channel surface so as to enhance the electricity production efficiency of the fuel cell. The gas flow channel surface is provided with a plurality of flow channels, and each of the plurality of flow channels is provided with a plurality of bends. Furthermore, the bend connecting lines of the flow channels are formed as linear shape and arrow shape, and the tips of the arrow shape are located on the same horizontal line. When the two partition plates are joined together by the coolant flow channel surfaces, the grooves of the two coolant flow channel surfaces are formed as linear flow channels for conveying cooling agent. However, the abovementioned structure having the plurality of bends on the gas flow channel surface may increase resistance to gas flow when the fuel gas (e.g. hydrogen), oxidant (e.g. oxygen) and the like flows in the flow channels for reaction and thus reduces electricity production efficiency.